Crater lamp



Feb. 19, 1 935- c. P. BROCKWAY CRATER LAMP Filed 001:. 28, 1952 INVENTOR. CARL F? BRqcA'm/Ay BY MM A TTORNEY Patented Feb. 19, 1935 UNITED/STATES PATENT OFFICE National Television Corporation,

Wilmington,

DeL, a corporation of Delaware Application October 28, 1932, Serial No. 639,972

9 Claims.

This invention relates to gaseous discharge lamps of the crater type and has for its principal object to provide a crater lamp having a concentrated intensely bright discharge.

vide a discharge lamp with means to augment the light produced by the discharge.

Other objects of the invention and objects relating particularly to the construction and assembly of the various parts of the lamp will be apparent as the description proceeds.

The invention is illustrated in the accompanying drawing in which:

Fig. 1 is a sectional elevational view of one form ofthe invention which may be preferred;

Fig. 2 is a front elevational view of the lamp shown in Fig. 1;

Fig. 3 is an enlarged fragmentary sectional elevational view of a cathode illustrating another embodiment of the invention; and

Fig. 4 is an enlarged fragmentary sectional elevational view of still another modified form of ,cathode.

10 of glass or other suitable transparent material fused in the usual manner to an inturned press 11 upon which are mounted the elements of the lamp. A cathode 12 is mounted as by welding, upon a support rod 13 which is sealed in the press 11 and to the end of which may be connected a lead-in wire 14 for making an external connection thereto. Spaced from the cathode is an anode 15 which may be welded or otherwise attached to a support rod 16 also sealed in the press 11 and to which a lead-in wire 17 is attached.

The cathode 12 may comprise a block 18 of any convenient shape and composed of a metal having a good conductivity and capable of being easily exhausted of occluded gases. Such a metal may be any one of the refractory metals, such as tungsten, molybdenum, tantalum, or other metals may be used such as iron, nickel or even copper. A cavity or crater 19 may be formed in one side of the block 18 and is preferably shaped so that its side walls form a parabolic curve, and is polished to give it a reflecting surface. I have found that the points of greatest intensity of light in a crater lamp are those points at which'the largest number of electrons appear to collide. I therefore form the crater with a parabolic curve so that all electrons leaving the surface of the crater in a direction normal to the surface will collide at a central line passing 5 through the focus 20 of the parabola. This line therefore becomes an intense region of illumination when the lamp is operated.

The anode 15 may comprise a metal disc, as indicated, which is spaced a short distance from the crater side of 'the cathode and is provided with a hole 21 directly in front of the center of the crater 19 so that the light formed therein can be viewed through the hole 21 in the anode. The anode may be formed of the same metal as the cathode, if desired, although this is not important.

I preferably coat the cathode and the support rod 13 with a layer 22 of a material which will tend to prevent the discharge forming thereon, such as an insulating material, or a coating of carbon or lamp black will be suflicient, as this appears to cut down the electron emission. The inside of the crater is left bare so that most of the emission arises from the crater.

.While the parabolic curvature in the crater shown in'Fig. 1 may be preferred, I may also form the crater as shown in Fig. 3, where the cathode 23 has a spherically curved crater 24 with the center of curvature at about the plane of the side of the cathode. Here the collision of electrons occurs at the center of curvature. In Fig. 4 another shape of crater is illustrated where the cathode 25 is provided with a cone-shaped crater 26. In this case, however, the intense region of illumination would not tend to form a point but would rather form a line extending outwardly from the apex of the cone. In both of these modifications a suitable coating 22 is provided to cut down the emission from the outer parts of the cathode.

With the elements assembled in a lamp in accordance with any of the embodiments illustrated above, the lamp may be connected in the usual manner to an exhaust pump and an oven placed over it to raise the temperature thereof so as 45 to drive out occluded gases from the envelope and elements. When the gases have been removed from the lamp I admit a small amount of an ionizable gas at a relatively low pressure. One of the monatomic gases such as neon, argon, 5o helium, krypton, and xenon may be used, although mixtures ofv these gases together or with other gases may be found expedient. For producing color effects or for increasing the conductivity of the gas a metal vapor may be added such as the vapors of mercury, caesium, rubidium, sodium, and the like. The gas is admitted at a pressure preferably below 15 mm. of mercury.

An intense white illumination was obtained with a lamp which was supplied with gases in the following manner: After the bulb had been exhausted, helium gas was admitted very slowly until a bright discharge was obtained with the plate andcathode connected in a circuit. Then a small amount of neon was admitted until the discharge turned to an orange color whereupon helium was again admitted until the pressure was too high and cut the discharge completely. Then the pump was turned on very slowly and allowed to withdraw some of the gases until a white concentrated light appeared through the hole in the anode. The bulb was then sealed 05 and was ready for use. This lamp was operated at approximately 200 volts with a current oi about 30 milliamperes. The discharge appeared as an intense point of light centered within the crater in the cathode making the lamp adapatable for television use or for recording sound-on-fllm or for any other use where modulated light is necessary. s

The light appearing through the hole in the anode arises not only from the point of intense illumination at the focus of the crater, but also as reflected light from the walls of the crater. As the point of intense illumination is at the focus of the crater, which is actually a parabolic reflector, the light which would ordinarily pass inwardly to be absorbed in the metal is sent out as a beam augmenting the light projected directly out by the discharge.

Modifications of the invention maybe resorted to without departing from the spirit thereof, and I do not, therefore, desire to limit myself to what has been shown and described except as such limitations occur in the appended claims:

What I desire to secure and claim by Letters Patent is:

1. A crater lamp having a cathode with a parabolically curved crater.

2. A crater lamp comprising a cathode having a crater, the surface of which is so formed that all lines drawn normal to the surface will pass through the same point.

.3. A crater lamp comprising an envelope, a

cathode within said envelope, a crater in the side of said cathode and having a surface such that all lines drawn normal thereto will pass through the same point, an anode spaced from said cathode and having an opening therein which is aligned with the crater.

4. A crater lamp comprising an envelope, a cathode within said envelope, a crater in the side of said cathode and having a parabolic surface, an anode spaced from said cathode and having an opening therein in alignment with said crater, and an ionizable gas containing neon surrounding said cathode and anode.

5. A crater lamp comprising an envelope, a cathode within said envelope, a crater in the side of said cathode and having a surface so curved that all lines drawn normal thereto will pass through the same point, an anode spaced from said cathode and having an opening in alignment with said crater, and an ionizable gas containing neon and helium within said envelope.

6. A crater lamp comprising a cathode, a crater in the side of said cathode having a portion of its surface in the form of a parabola, and an anode spaced from said cathode and having an opening therein in alignment with said crater.

7. A crater lamp comprising an envelope, a cathode within said envelope, a crater within said envelope and having a spherical curvature, an-

anode spaced from said cathode, and an ionizable gas containing neon surrounding said anode and cathode.

8. A crater lamp comprising a cathode coated with an electron discharge resisting material, an uncoated crater in the side of said cathode having a portion. of its surface in the form of 'a parabola, and an anode spaced from said cathode and having an opening therein in alignment with said crater.

9. A crater lamp comprising a cathode coated with an electron discharge resisting material, an uncoated crater in the side of said cathode having a portion of its surface in the form of a parabola, and an anode spaced from said cathode and having an opening therein in alignment with said crater, said opening having a diameter less than that of the outer end of the crater.

' CARL P. BROCKWAY. 

